Pharmacology

Indication

The primary known function of vitamin K is to assist in the normal clotting of blood, but it may also play a role in normal bone calcification.

Pharmacodynamics

Menadione (Vitamin K3) is a fat-soluble vitamin precursor that is converted into menaquinone in the liver. Vitamin K1 and K2 are the naturally occurring types of vitamin K. The former, which is also known as phylloquinone, is synthesized by plants and can be found in such foods as spinach, broccoli, lettuce, and soybeans. The latter, sometimes alternatively referred to as menaquinone, is primarily produced by bacteria in the anterior part of the gut and the intestines. Vitamin K3, on the other hand, is one of the many manmade versions of vitamin K. Also called menadione, this yellowish, synthetic crystalline substance is converted into the active form of the K2 vitamin inside of the animal body. While a vitamin K deficiency can be dangerous, especially to infants that may easily suffer from extensive hemorrhaging, an overdose can be as equally detrimental. Newborns that are administered too great a dosage of vitamin K3 can suffer from kernicterus, a form of severe brain damage that may produce decreased movement, loss of appetite, seizures, deafness, mental retardation, and even death. This condition is associated with an abnormally high concentration of bilirubin, a bile pigment, in the tissues of the brain, which can be caused by the presence of K3. For this reason, K3 is less often utilized medically than it was in former times.

Mechanism of action

Menadione (vitamin K3) is involved as a cofactor in the posttranslational gamma-carboxylation of glutamic acid residues of certain proteins in the body. These proteins include the vitamin K-dependent coagulation factors II (prothrombin), VII (proconvertin), IX (Christmas factor), X (Stuart factor), protein C, protein S, protein Zv and a growth-arrest-specific factor (Gas6). In contrast to the other vitamin K-dependent proteins in the blood coagulation cascade, protein C and protein S serve anticoagulant roles. The two vitamin K-dependent proteins found in bone are osteocalcin, also known as bone G1a (gamma-carboxyglutamate) protein or BGP, and the matrix G1a protein or MGP. Gamma-carboxylation is catalyzed by the vitamin K-dependent gamma-carboxylases. The reduced form of vitamin K, vitamin K hydroquinone, is the actual cofactor for the gamma-carboxylases. Proteins containing gamma-carboxyglutamate are called G1a proteins.

Menadione (vitamin K3), which is not used as a nutritional supplemental form of vitamin K for humans, has been reported to cause adverse reactions, including hemolytic anemia. Large doses have also been reported to cause brain damage.

Taxonomy

Description

This compound belongs to the class of organic compounds known as naphthoquinones. These are compounds containing a naphthohydroquinone moiety, which consists of a benzene ring linearly fused to a bezene-1,4-dione (quinone).